Photon-phonon coupling through guided-wave stimulated Brillouin scattering (SBS) is finding application in numerous technology fields such as tailorable slow light, radio frequency (RF)-photonic signal processing, narrow-line-width laser sources, RF-waveform synthesis, optical frequency comb generation, etc. Realization of this form of travelling-wave photon-phonon coupling in a silicon-based and CMOS (complementary metal-oxide-semiconductor)-compatible platform can enable high-performance signal-processing applications through nanoscale Brillouin interactions. Nanoscale modal confinement can enhance non-linear lightmatter interactions within silicon waveguides and in nanooptomechanics. For instance, tight optical confinement in nanoscale silicon waveguides can be responsible for greatly enhanced Raman and Kerr non-linearities, and for new sensing, actuation and transduction mechanisms based on optical forces within nano-optomechanical systems.
The field of cavity optomechanics has produced a wide variety of systems with enhanced and controllable forms of photon-phonon coupling. Specifically, silicon (Si)-based cavity optomechanical systems have enabled powerful new forms of quantum state transfer, slow light, phonon lasers and optomechanical ground-state cooling. Such cavity systems exploit resonantly enhanced coupling between discrete photonic and phononic modes. As a fundamental complement to cavity systems, guided-wave Brillouin processes can produce coupling between a continuum of photon and phonon modes for a host of wideband (e.g., 0.1-34 GHz) RF and photonic signal-processing applications. For example, travelling-wave Brillouin processes have enabled unique schemes for optical pulse compression, pulse and waveform synthesis, coherent frequency comb generation, variable bandwidth optical amplifiers, reconfigurable filters and coherent beam-combining schemes. Although there are numerous applications and opportunities for chip-scale Brillouin technologies, the ability for conventional systems to achieve Brillouin processes in silicon nanophotonics has proven difficult; strong Brillouin nonlinearities require large optical forces and tight confinement of both phonons and photons, conditions that are not met in conventional Si waveguides.